Module 15: spectrometer and it’s parts


spectrochemistry - Measures the chemical substance by measuring the amount of light absorbed through a light intensity that passes through the solution

spectrophotometry - U want to know the Quantity, composition (machine measure glucose level of serum)


7 parts of spectrophotometer

  1. Light source

  2. Entrance slit

  3. Monochromator

  4. Exit slit

  5. Cuvet (sample solution)

  6. Detector

  7. Meter/ Digital Display

(Meanings)

1. Light source- provides poloychromatic light and generate sufficient energy to measure the analyte of interest.

2 types of light source

  • Continuum source -exits radiation changes in intensity, widely used Ex. Tungsten, deuterium, xenon lamps

  • Line source - emits limit radiation and wavelength. Ex. Mercury, hallow cathode lamp


2. Entrance slit - minimizes unwanted or stray light and prevents the entrance of scattered light


3. Monochromator - isolates specific or individual wavelengths of light

Kinds of monochromator

  • Prisms - can be rotated, allowing only the desired wavelength to pass through the cuvet

  • Diffraction gratings- most commonly used; better resolution that prism

  • Filters (used in photometer) - simple, least expensive, not pre-use but useful

  • Holographic gratings


4. Exit slit - controls the width of light beam (bond pass) allows only a narrow fraction of the spectrum to reach the sample cuvette.


5. Cuvette - Also called absorption cell/ analytical cell/ sample cell , It holds the solution whose concentration is to be measured

kind of cuvette

  • Alumina silica glass- most commonly used

  • Quartz- used for measurement of solution requiring visible and ultraviolet spectra

  • Borosilicate glass

  • Soft glass


6. Photodetector - detect and converts transmitted into photoelectric energy. Detect the amount of flight that passes to the sample in the cuvet

Kinds of detectors

  • Barrier layer cell/ photocell/ photovoltaic cell - The simplest detector least expensive and temperature sensitive

  • Photo tube

  • Photo multiplier tube (pmt) - most common use detector

  • Photodiode - Not as sensitive as PMT, but with excellently linearity


  1. Meter/digital display- it displays output of the detection system. Ex. Emitting diode (LED) display


Alternatives for tungsten bulb

  1. Mercury arc (visible, UV)

  2. Deuterium lamp (UV)

  3. Hydrogen lamp (UV)

  4. Xenon lamp (UV)

  5. Merst glower (IR)

  6. Globar (IR)


Regions

<400 - ultraviolet

400-700 - visible spectrum

>700 - Infared region


Two types of spectrophotometer

  • Single beam spectrophotometer - simpliest type


  • Double beam spectrophotometer - Splits monochromatic light into 2 components. One that passes to the sample, other is passed, then a reference solution blank

    Two types of Double beam spectrophotometer

    1. Double beam in space - uses 2 photodetectors ( 1 sample beam, and 1 reference beam)

    2. Double beam in time - uses one photo detector and alternately passes The Monochromatic light thru cuvet and reference Cuvet using a CHOPPER/ ROTATING SECTOR MIRROR